An example of a diaphragm valve structure which was commonly conventionally employed is shown in FIG. 5. The diaphragm valve structure in FIG. 5 regulates the flow of a fluid between flow passages 21 and 22. This regulation is conducted by means of a valve seat 53, which is provided around the circumference of the opening of flow passage 21, and a diaphragm 52, which conducts the opening and the closing of this opening by means of valve seat 53. External operation is conducted by means of rotating a handle 54.
The details of the portions surrounding the diaphragm of this conventional example are shown in FIG. 6. In FIG. 6, valve seat 53 has a caulked seat structure, and the base portion of the valve seat is embedded in a body 57 at the circumference of the opening of flow passage 21 so as to be circular and concentric with this opening, and the valve seat is thus supported.
The open and closed states of the opening of flow passage 21 are formed by means of the positional relationship between diaphragm 52 and valve seat 53, which is disposed around the circumference of the opening of flow passage 21 so as to have a cross-sectionally convex shape. In the state which the diaphragm 52 is not pressed downward by means of holder 56, the diaphragm 52 is not in contact with valve seat 53, and an open state is formed in which space is present at the opening of the flow passage 21. Furthermore, when the handle 54 is rotated and holder 56 descends along body 57, diaphragm 52 is pressed downwards and comes into immediate contact with valve seat 53, thus forming a closed state.
FIG. 7 shows another conventional structural example. In this example, seat holder 61 presses against valve seat 63 from above, and valve seat 63 is thus affixed to body 67. The basic structure of flow passages 21 and 22, diaphragm 52, body 67, and the like are identical to those in the conventional example described above. Commonly, valve seat 63 is formed from resin, while seat holder 61 is formed from metal.
However, PCTFE (Poly Chloro Tri Fluoro Ethylene) is employed as the material of valve seats 53 and 63 in order to increase the air tightness as described above; however, creep occurs with repeated operation. This phenomenon occurs more noticeably when heat is applied to the resin, or when the resin is exposed to a halogen-type gas, and thus the occurrence of the phenomenon of the decrease in the strength of the valve seat is promoted.
That is to say, in the case of the conventional example first described above, the valve seat 53 is unable to withstand the force of the drive unit, is deformed, and thus creep is generated, the amount of valve lift increases, and the phenomenon proceeds to the rupture of diaphragm 52. There are valve structures in which, as a countermeasure to this problem, a lift stopper is provided at diaphragm 52; this lift stopper restricts the range of movement so that valve lift above a fixed amount does not occur. However, when the lift stopper described above operates in the state in which valve seat 53 has no reaction force, the occurrence of valve seat leakage is unavoidable. Furthermore, in the diametrical direction of diaphragm 52, this lift stopper is provided at a position separated from valve seat 53. For this reason, there is a large variation in the point at which the lift stopper 54 operates. Furthermore, in the case of the second conventional example described above, since the valve seat 63 has a structure which is sufficiently capable of withstanding the force of the drive unit, the amount of creep which occurs is limited; however, on the other hand, this involves a greater disadvantage in that the resinous valve seat 63, which is a source of gas contamination, is large.
When such conventional examples are employed in lines requiring high precision, such as semiconductor production lines or the like, the various defects described above become unavoidable problems.
The present invention has as an object thereof to provide a diaphragm valve structure possessing high durability and reliability.